Perfect chitin is an item obtained from the Kalphite King. The chitin is only dropped when an ancient defender, repriser or lantern or a better defender[1] is equipped or in the player's inventory.
The chitin is used to create defenders, by combining it with new or fully repaired tier 90 off-hand weapons.
In a LootShare kill, the chitin goes to the "LootShare points leader," the one with the highest points, who is able to receive the chitin drop. The player must also be one of the top-16 players of damage dealt to the boss during that kill. Since the chitin drop is low-value and is in a drop table before drops, the player can likely receive the chitin without losing their chance at other Kalphite King drops.
^Jagex. Mod Chaose's Twitter account. 18 November 2015. Mod Chaose: "You need a dragon defender or above to get the t70 component, any of the t70 defender or above to get the t80 component and so on."